1. Field of the Invention
This invention relates to steam generators and more particularly, relates to a compact, small volume steam generating system.
2. Background Information
Portable steam generating systems are used for steam cleaning in restaurant kitchens, hotel/motel bathrooms, public bathrooms, rest homes, hospitals, dental offices and related human services facilities. They are also used in industry for cleaning dirty and contaminated surfaces of oil and grease, and also for steam cleaning vehicle engines. Steam generating systems are also used for the removal of paint, wallpaper, graffiti, etc.
Heavy duty steam cleaning equipment has been available for many years for heavy and medium cleaning. However, a lengthy and in-depth study revealed almost a complete lack of small, portable, lightweight, low capacity steam cleaning equipment for small items and limited surface areas in confined spaces. To date, only a few foreign and United States companies supply such equipment.
The only U.S. producer of a low capacity steam cleaner was found to be a system that has a small tank (≈500 in3), having a 1,500 to 2,500 watt heater with a fill valve and a steam discharge valve as shown in FIG. 1. The system also includes a pressure relief valve and a low water liquid level cut-off switch for safety purposes. The operating parameters provide a pressure up to 200 PSI, and a temperature up to 350xc2x0 F. Generally, the water tank shown in FIG. 1 has a capacity of approximately three quarts. The steam flow provided is in the range of about 0.005 to 0.007 gallons per minute (GPM). A problem with this type of system is that it can take up to thirty minutes from a cold start to reach operating temperature and pressure. Since the system is made to be portable, the water supply is intermittent at about three quarts per filling for a run time per filling of one to three hours.
This type of small, light weight and low capacity system has a number of operational limitations and one very serious safety problem. The system is limited by it""s low water volume since only three quarts of water can be used at any one time, then the system must be powered down, pressure reduced to atmospheric and then refilled with fresh water. It also suffers with the problem of a long heat-up time; typically thirty minutes before any steam is generated. The steam tank, being a substantial size and having a water capacity of only three quarts, has a large, heavy, thick-walled and expensive certified steam pressure vessel.
The serious safety problem is because the super-heated steam/hot water combination can explode to a substantial volume if a tank failure occurs. Generally, the steam explosion can be on the order of 200 times the tank volume. A typical commercial unit, as shown in FIG. 1, has a 7xe2x80x3xc3x9713xe2x80x3 cylindrical tank with a volume of 500 cubic inches, which could produce a steam plume of approximately 100,000 cubic inches (expansion ratio of 200) which is of sufficient size to injure anyone within 4 to 5 feet of the tank wall. A 7xe2x80x3xc3x9713xe2x80x3 tank with a standard wall thickness of 0.034 inches, 304 type stainless steel has a Barlow burst pressure of approximately 2,400 pounds per square inch (PSI) and a safety factor of approximately twelve (12). Using a flat welded end of the pressure tank can reduce the safety factor to below 3.
The end result of a study of existing small portable steam cleaners is as follows: 1) All units are heavy and bulky. 2) Have severely limited water supplies. 3) Units must be shutdown, depressurized and cooled to replace the water supply. 4) Units must use expensive heavy wall tanks to contain super-heated steam. 5) Have lengthy (≈30 minute) start-up times. 6) Require tank certification to steam boiler codes. 7) Contain from three quarts or one to 6 pounds of super-heated steam during operation. 8) Have operating energy potential to expand explosively if ruptured with concomitant injury to operating personnel and nearby persons.
Therefore, it is one object of the present invention to provide an efficient steam generator that is small in size and has an extremely low (≈2xc3x9710xe2x88x926 Gal or 2xc3x9710xe2x88x925 lbs) super-heated steam volume in the boiler at any given time during operation.
Still another object of the present invention is to provide a steam generating system that can be light in weight, yet provide unlimited continuous supply of steam.
Yet another object of the present invention is to provide a steam generating system that has an extremely short transient heat-up time. For example, a steam generating time of three to five minutes from a cold start.
Yet another advantageous object of the invention is to provide a light weight, low capacity steam generating system that can be refilled while in use, thus providing continuous steam supply.
Yet another object of the present invention is to provide a light weight, low volume steam generator that has a design that is inherently fail safe because it has a cylinder rupture safety factor many times larger (S.F. ≈39) than that of present systems.
Still another object of the present invention is to provide a light weight, low capacity steam generator system that has a reduction in operating super-heated steam weight by a factor of approximately 0.5 million.
Still another object of the present invention is to provide a light weight, low capacity steam generating system that has the important major inherent safety design feature of a continuous open ended flow from the water supply to the steam generator to the outside world.
Yet another object of the present invention is to provide a light-weight, low capacity steam generating system that includes a method of preventing water droplets from being ejected with the steam from the system.
Still another object of the present invention is to provide a light-weight, low capacity steam generating system that includes an extension at the outlet that minimizes ejection of water droplets into the steam.
Yet another object of the present invention is to provide a light-weight, low capacity steam generating system having an end formed on the extension that minimizes the injection of water droplets into the steam.
Still another object of the present invention is to provide a light-weight, low capacity steam generating system having a method of maintaining the temperature and pressure of the super-heated steam from the steam generator outlet to a cleaning tool.
Still another object of the present invention is to provide a light-weight, low capacity steam generating system having a special coaxial output hose configured to substantially reduce steam heat loss to the atmosphere during transportation of steam from the steam generating cylinder to an application tool or brush.
Yet another object of the present invention is to provide a light-weight, low capacity steam generating system having an insulation plastic tube over a smaller diameter Teflon tube as a thermal insulator to physically shield and protect against abrasion during use.
Still another object of the present invention is to provide a light-weight, low capacity steam generating system having a small diameter, output tube wound around a steam generating cylinder to maintain the temperature of the super-heated steam and increase the thermal conductivity from the outlet to the application tool or brush.
The purpose of the present invention is to provide a light weight, low capacity steam generating system that is very portable and safe to use. The present invention addresses and solves all eight deficiencies of current small portable production steam cleaning units listed above.
The invention described uses two different applications based upon a single approach to efficiently and rapidly transfer heat energy from a hot source to a body of water or related type fluid. The hot source is normally a resistive wire (nichrome, etc.) coil or hot gas such as a methane gas heater flame. While the disclosure is focused upon electric wire heating rods, the principles and techniques apply equally as well for gas fired heated rods and tubes.
The basic technical approach employed is to heat a small quantity of working fluid such as water, in as brief a time as possible. For example, one ounce to one pound of water in a time span of a few seconds to several minutes (one to ten minutes).
The system uses approximately a one foot long hollow cylinder having a central located heater body and a plurality of baffles spaced along the interval length of the volume. Water is injected at an input and flows through a series of time delay turbulent creating baffles positioned in the heating cylinder to form a diffused flow path of variable length and dwell time as it passes from the input to the exit. In the steam generating mode the diffused spiral flow path will cause the small amount of water injected at the input to be converted to steam as it is transported to the output port.
Preferably, the baffles are equally spaced along the cylinder and cause the fluid flow path to alternate through a series of control orifices or ports from a position adjacent to the hot outside diameter (OD) surface of the cylindrical, centrally located heater to the inside diameter (ID) surface of the cylindrical steam chamber. The ports or orifices in adjacent ring shaped baffles, are shaped and sized and are at 180xc2x0 to one another to increase turbulent mixing of the water or fluid, converting it to vapor/steam combination as it passes from the input to the output. The combination of adjacent baffles, heater OD and steam chamber support ID produces a series of alternating orifice generating steam jet expansion and orifice steam jet compression subsystems that maximize the heat transfer from the cylindrical heater body to the working fluid converting the fluid to steam at the output.
The steam jet compression/expansion sequence in combination with the interbaffle volume, is a critical element of the invention in that it produces intimate turbulent scouring of the developing steam jet over the entire internal surfaces of the baffle volume segments and the external surface of the cylindrical heater maximizing dynamic heat transfer coefficients. Thus, the external surface of the cylindrical heater converts the working fluid to clean dry droplet free steam or wet steam as required at the output.
Another unique feature of the invention is the provision of a variable pressure open ended pressure regulating control valve on the steam output port. This allows the pressure and flow volume of the steam output of the heater/baffle system to be controlled while providing for an always xe2x80x9copenxe2x80x9d flow through system (i.e., no possibility of a closed steam valve between the input and output). It also allows further regulation of the overall vapor/steam dwell time for the formation of the steam at the output in the steam support tube. Further, the variable control valve allows control of output pressure (e.g., 10 to 200+ PSI) of the steam cleaning jet as required by each cleaning situation and environment.
Another essential element of the invention is to provide an adjustable low flow rate capability (e.g., near 0 to 1.0+) gallons per minute (GPM) by means of a pulse type pressure pump (25 to 500 PSI) injecting feed water into the coaxial steam chamber input at a pressure determined by the open ended output variable pressure control valve.
Research into pumps reveal that there are no industrial fluid pump suppliers (Thomas Register of American Manufacturers and related publications) capable of providing the very low flow rates at the pressure required. Therefore, the present invention includes a newly designed pulse type pump to supply the pressure performance and flow capacity described above.
The fluid pump design consists of a forward and aft sliding piston driven by a rotating variable diameter eccentric, driven at a constant speed by a rotary motor. An input check valve, in combination with an output check valve, motor and piston produce a pulsed water flow output. The volume of water delivered to the steam generating cylinder and support tube at the input can be adjusted by adjusting the diameter of the pump piston, the stroke of the eccentric arm and the RPM of the drive motor. A typical set of various combinations of motor RPM, piston diameter and piston stroke, provide a wide range of fluid pumping rates (e.g., from near 0 to 1.0+ GPM or more at pressures from near 0 to 500 PSI or more).
The operational life of the cylindrical heater (i.e., watt density) is a function of the heat input rate and heat extraction rate of the fluid being heated. The series of baffles, with alternating ports disclosed herein, is specifically designed to maximize heat transfer to the working fluid; thus, the heater""s internal coil wire design is limited by the maximum continuous temperature of the internal coil resistance wire, (i.e., watt density) which can be up to dull red. Thus, the system disclosed herein provides a very long heater life due to programmed low to medium coil temperatures (i.e., watt density), steam tube diameter and length for various steam generating applications without a major redesign of the steam generating dimensions. Long heater life is also enhanced by the selection of high temperature metal support tubes preferably of copper or tubes with good to excellent high temperature corrosion resistance (e.g., Incoloy 316SS, 304SS, etc.).
The steam pressure cylinder surrounding the heater can vary from copper to aluminum, to stainless steel, etc. The system described can provide a Barlow steam tube bursting pressure of up to 5,833 PSI or more and a safety factor of up to nineteen (19) or more, which is substantially above current U.S. portable steam cleaning equipment.
In an optional embodiment of the invention, the plurality of baffles are replaced by single baffles at each end of the cylinder with water flowing through counter-revolution coils surrounding the centrally located heater. Water flows in through the first baffle along the length of the cylinder into the tubular coil at the opposite end. The water is then heated to steam by flowing back to the opposite end of the cylinder through two coils and then back through an outlet port. The double convoluted coils are arranged for the water to be converted to steam by three passes over the heating element. The first pass is through the cylinder while the second and third passes are through the wound copper coils from an inlet to an outlet.